Temperature control system



y 1940- w. J. MCGOLDRICK .ET AL 2,200,241

TEMPERATURE CONTROL SYSTEM Filed Jan. 7, 1939 {inventors William J. M'Goldrick Alwin B. New-1 on.-

Patented May 14, 1940 TEMPERATURE CONTROL SYSTEM William J. McGoldrickand Alwin B. Newtonp Minneapolis, Minn., assignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation ofDelaware Application January 7, 1939, Serial No. 249,764

. 14 Claims.

This invention relates in general to temperature control systems formaintaining desired temperature conditions in a plurality of spaces andmore particularly to a temperature control 5 system for a refrigeratingapparatus for maintaining desired temperature conditions in a pluralityof spaces or fixtures being cooled.

An object of this invention is to provide a control system for atemperature changing apparatus which regulates the temperature in aplurality of spaces wherein the temperature changing apparatus isoperated when the temperatures in all of the spaces deviate topredetermined values and wherein the temperature 18 changing apparatusis operated if the temperature in any space deviates beyond thepredetermined value.

Another object of this invention is to provide a control system .for amultiple fixture refriger ating apparatus having thermostatic control-means responsive to the temperature of the fixtures and control meansresponsive to evaporator temperatures to operate the refrigeratingapparatus upon a call for cooling by the thermostatic control means andto defrost the evaporators upon each cycle of operation of therefrigerating apparatus wherein the refrigerating apparatus is placed inoperation when the temperatures in all of the fixtures increase to'pre-30 determined values and wherein the refrigerating apparatus'is placedin operation when the temperature in any fixture increases above thepredetermined values. This sequence of temperature control causes all ofthe fixtures to heat and 5 cool substantially together so that therefrigerating apparatus is not maintained in continuous operationwhereby periodic defrosting of the evaporators is assured.

Other objects reside in the structure and man- 40 ner of accomplishingthe above sequences of control.

For a more thorough understanding of this invention, reference is madeto the accompanying drawing in which is diagrammatically illus- 5 tratedthe preferredform of this invention.

Although the control system of this invention may be equally as wellapplied to any type of temperature changing system, such as a heatingsystem, it is shown as applied to a multiple fix- 50 ture refrigeratingsystem for maintaining desired temperature conditions in a plurality offixtures or spaces III, II and I2 which may take the form of rooms,walk-in boxes, storage compartments, soda fountains, or the like. Thefixtures or spaces I8, II and I2 are cooled by which may comprise acompressor I'I operated by an electric motor I8. Compressed refrigerantflows from the compressor I! through a high 1 pressure line I9 into acondenser 20 and condensed refrigerant is collected in a receiver 2|.Liquid refrigerant flows from the receiver 2| through a liquid line 22into the evaporators I3, M and I5, and evaporated refrigerant iswithdrawn from the evaporators I3, I4 and I5 through a suction line 23by the compressor I1. It is here noted that the evaporators I3, l4 andI5 are arranged in parallel. The flow of refrigerant into theevaporators I3, I4 and I5 is regulated by expansion valves 24, 25 and26, respectively, which may take the form of thermostatic expansionvalves ofv a conventional type. Since the above outlined structure isconventional in the art, a further description thereof is not considerednecessary, it being suflicient to state that when the compressor I1 isplaced in operation refrigerant is supplied to the evaporators I3, I4and I5 to perform a cooling function.

The supply of refrigerant to the evaporators I3, I4 and I5 is controlledby solenoid valves 21, 28 and 23, respectively, the arrangement beingsuch that when the solenoid valves are opened and the compressor is inoperation refrigerant is supplied to the evaporators and when thesolenoid valves are closed the supply of refrigerant to the evaporatorsis interrupted. The solenoid valves 21, 28 and 29 are controlled bythermostatic control means 3|, 32 and 33 responsive to the temperaturein the fixtures I8, I and I2, respectively. The compressor motor I8 andhence the compressor I! are controlled by the thermostatic control means3|, 32 and 33,

and in addition the compressor motor I8 and hence the compressor I! arecontrolled by a unitary control arrangement generally designated at 34,this unitary control arrangement being operated in accordance withchanges in mercury switch 39 having electrodes 4| and 42 which arebridged upon a temperature rise and the mercury switch 40 havingelectrodes 43, 44

and 45 which are also bridged upon a temperature rise. For purposes ofillustration it is assumed that the parts are so arranged that when thetemperature within the fixture I0 rises to 42, the mercury switches 39and 40 are tilted to a position to cause bridging of the electrodes 4|and 42 and bridging of the electrodes 43 and 44. It is here notedthat'the electrode 45 is shorter than the electrodes 43' and 44 so thatthe electrode 45 is not bridged until such time as the temperaturewithin the fixture In increases to, say 44. At 44 electrodes 4| and 42are bridged and the electrodes 43, 44 and 45 are bridged. When thetemperature within the fixture |0 decreases to 40, the mercury switches39 and 40 are tilted to the position shown in the drawing to unbridgethe electrodes. The thermostatic control means 32 and 33 are exactly thesame as the thermostatic control means 3| and therefore like referencecharacters for like parts have been utilized. It is of course obviousthat the temperature settings of the thermostatic control means 32 and33 may be other than that of the thermostatic control means 3| so thatany desired temperature may be maintained within the various fixtures.

The unitary control arrangement 34 may be of the type shown anddescribed in application Serial No. 196,447 filed by Albert L. Judsonand Carl G. Kronmiller on March 17, 1938. For purposes of illustrationin this application the unitary control arrangement 34 is shown tocomprise a switching mechanism generally designated at 48 responsive tovariations in suction pressure, a switching mechanism generallydesignated at 49 responsive to variations in head pressure, an overloadcut-out generally designated at 50, and a relay or starter generallydesignated at 5|.

The switching mechanism responsive to variations in suction pressure maycomprise a bellows 53 connected by a pipe 54 to the suction line 23 sothat the bellows 53 is expanded and contracted in accordance withvariations in suction pressure. The bellows 53 operates a lever 55fulcrumed on fulcrum member 56 against the action of an adjustabletension spring 51. One end of the tension spring 51 is connected to thelever 55 and the other end is connected to a nut 58 screw-threadedlymounted on a screw 59. By rotating the screw 59 the tension in thespring 51 may be varied and hence the pressure setting of this portionof the instrument may be adjusted. Lever 55 carries an insulating pad 60upon which is mounted a bridge member 6| for operating contacts 62 and65. The contact 62 is adapted to engage a contact member 63 suitablymounted on a terminal 64 and the contact 65 is adapted to engage acontact member 66 suitably mounted on a terminal 61. The relativepositions of the contact members 63 and 66 may be adjusted by means ofconcentrically mounted cams 68 and 69 which are independentlyadjustable. For purposes of illustration it is assumed that when thesuction pressure increases to 10 lbs. contact 62 engages contact member63, and when the suction pressure increases to 35 lbs. contact 65engages contact member 66. Upon a decrease in suction pressure contact65 first disengages contact member 66 at 35 lbs. and then contact 62disengages contact member 63 at 10 lbs.

The switching mechanism 49 responsive to variations in head pressure maycomprise a bellows 12' connected by a pipe I3 to the high pressure tact84.

line I9 so that the bellows "I2 is expanded and contacted in accordancewith variations in head pressure. The bellows I2 operates a lever 14fulcrumed on a fulcrum member I5 against the action of an adjustabletension spring I6. One end of the tension spring I6 is connected to thelever 14 and the other end is connected to a nut 11 screw-threadedlymounted on a screw I8. By rotating the screw I8 the tension in thespring I6 is varied and hence the pressure setting of this portion ofthe unitary control arrangement may be adjusted at will. The lever I4adjustably carries an abutment member I9 provided with abutments and BI.The abutment 80 is adapted upon a pressure increase to engage a contactmember 82 carried by a terminal 83 to separate the contact member 82from a stationary con- The abutment member 8| is adapted upon a pressureincrease to engage a contact member carried by the terminal 61 to causethe contact member 85 to disengage a stationary contact 86. For purposesof illustration it is assumed that upon a pressure increase the contactmember 85 first disengages the contact 86 at lbs. and then the contactmember 82 disengages the contact 84 at lbs. Upon a decrease in headpressure the contact member 82 first engages the contact 84 at 190 lbs.and then the contact member 85 engages the contact 86 at 140 lbs.

The overload cut-out 50 may comprise a terminal 89 and a contact 90between which is mounted a heater element 9|. The heater element 9|operates upon an excessive current flow therethrough, a bimetallicelement, not shown, for tripping a latch to separate contacts 92 and 93.Hence the contacts 92 and 93 are separated upon an overload condition.The contacts 92 and 93 may be reclosed by means of a manual lever 94.

The relay or starter 5| may comprise an operating coil 91 for operatinga bridge member 98 with respect to contacts 99 and I00 and a bridgemember |0| with respect to contacts 90 and I02. When the operating coil91 is energized the bridge member 98 is moved into engagement with thecontacts 99 and I00 and the bridge member IOI is moved into engagementwith contacts 90 and I02. When the operating coil 91 is deenergized thebridge members 98 and IN are moved out of engagement with theirrespective contacts by means of springs, gravity, or other means notshown.

The unitary control arrangement 34 also includes terminals I04 and I05which are connected to line wires I06 and I0! leading from some sourceof power, not shown. The line wires I06 and IN supply power to thecompressor motor l8, the solenoid valves 21, 28 and 29, and to thecontrol system.

Assume now that the temperature within the fixture I0 increases to 42 tocause the electrodes 4| and 42 and the electrodes 43 and 44 to bebridged. A circuit is thereupon completed from the line wire I06 throughterminal I04, wires I|0, III and H2, electrodes 43 and 44, wire H3,solenoid valve 21 and wires H4 and II 5 back to the other line wire I01.Completion of this circuit upon a temperature increase to 42 energizesthe solenoid valve 21 to open the same. The thermostatic control means32 and 33 of the fixtures II and I2 control their solenoid valves 28 and29 respectively, in exactly the same manner as the thermostatic controlmeans 3| controls its solenoid valve 21 and therefore like referencecharacters primed and double primed have been utilized forlike wiringconnections. A further description, therefore, of the operation of thesolenoid valves 28 and 29 is not considered necessary, it beingsufiicient to state that when the temperatures within the fixtures I Iand I2 increase to predetermined values the solenoid valves 28 and 29are opened.

Assume now that the head pressure decreases to 140 lbs. to cause thecontact member 82 to engage the contact 84 and the contact member 85 toengage the contact 06, that the suction pressure increases to 35 lbs. tocause the contact 62 to engage the contact member 63 and the contact 65to engage the contact member 66, and that the temperatures within all ofthe fixtures I0, It and i2 increase to the predetermined values,illustratively 42. A circuit is thereupon completed from the line wireI06 through terminal I04, Wires III], III and III, electrodes 4| and 42of the thermostatic control means 3|, wire II8, electrodes 4| and 42 ofthe thermostatic control means 32, wire II9, electrodes 4| and 42 of thethermostatic control means 33, wires I20, I2I, I22 and I23, contact 84,contact member 82, terminal 83, conductor I24, terminal 64, contactmember 63, contact 62, bridge member 6|, contact 65, contact members 66and 85, contact 86, conductor I25, contact I00, conductor I26, contacts92 and 93, conductor I21, operating coil 91, conductor I28 and terminalI05 back to the other line wire I01. Completion of this circuitenergizes the operating coil 91 to move the bridge member 98 intoengagement with its contacts 99 and I00 and to move the bridge memberIOI into engagement with its contacts and I02.

Movement of the bridge member IOI into engagement with its contacts 90and I02 completes a load circuit for the compressor motor I8 which maybetraced from the line wire I06 through terminal I04, conductor I30,terminal 89, heater element 9|, contact 90, bridge member IOI, contactI02, wire 'I3I, compressor motor I8, wire I32 and terminal I05 back tothe other line wire I07. Completion of this circuit causes operation ofthe compressor motor I8 and hence the compressor I I. Accordingly, whenthe temperatures in all of the fixtures increase to predeterminedvalues, illustratively 42, the compressor I! is placed into operationproviding the suction pressure has increased to 35 lbs. and the headpressure has decreased to lbs. For purposes of illustration it isassumed that a suction pressure value of 35 lbs. represents a defrostingvalue so that it is impossible to start the compressor I'I until suchtime as all of the evaporators I3, I4 and I5 have defrosted. It is alsoimpossible to start the compressor until such time as the head pressuredecreases to 140 lbs. whereby heavy starting loads on the compressormotor I8 are practically eliminated.

Movement of the bridge member 98 into engagement with the contacts 99and I00 completes a maintaining circuit for the operating coil 91 of therelay or starter 5| which is independent of contact 65, contact member66, contact 86, and contact member 85. This maintaining circuit may betraced from the line wire I06 through terminal I04, wires III], III andIII, electrodes 4| and 42 of the thermostatic control means 3|, wireII8, electrodes 4| and 42 of'the thermostatic control means 32, wireII9, electrodes 4| and 42 of the thermostatic control means 33, wiresI20, |2I, I22 and I23, contact 84, contact member 82,

suddenly in operation until such time as the temperature in any of thefixtures I0, I I or I2 decreases to 40 to unbridge the electrodes 4| and42 or until the head pressure increases to lbs. to move the contactmember 82 out of engagement with the contact 84 or until the suctionpressure decreases to 10 lbs. to move the contact 62 out of engagementwith the contact member 63. When any of these contingencies occur tostop the compressor I1, it cannot again be placed in operation until thehead pressure decreases to 140 lbs., the suction pressure increases to35 lbs. indicating that all of the evaporators I3, I4 and I5 havedefrosted and until the temperature of all of the fixtures I0, II and I2rise to the predetermined values, illustratively 42. Defrosting of allof the evaporators I3, I4 and I5 is therefore provided during each cycleof operation of the compressor I'I. Since the compressor I1 is notstarted until the temperature in all of the fixtures I0, IIand I2increases to the predetermined value, illustratively 42, the fixturesI0, II and I2 will tend to heat and cool at substantially the same timeso that periodic stopping of the compressor and hence periodic,defrosting of the evaporators is assured.

If, however, the load in the fixture I0 should increase to cause thetemperature thereof to rise above the predetermined value, say to 44,the electrodes 43, 44 and 45 of the thermostatic control means 3|, arebridged to complete a circuit from the line wire I06 through terminalI04, wires IIO, III and H2, electrodes 43 and 45 of the mercury switch40, wires I36 and I23, contact 84, contact member 82, terminal 83,conductor I24, terminal 64, contact member 63, contact 62, bridge member6|, contact 65, contact members 66 and 85, contact 86, conductor I25,contact I00, conductor I 26, contacts 92 and 93, conductor I2I,operating coil 91, conductor I28 and terminal I05 back to the other linewire I01. Completion of this circuit therefore pulls in the relay orstarter 5| to place the compressor IT in operation even though thetemperature within the fixtures 32 and 33 has not risen to thepredetermined values of 42. Accordingly, if the temperature in thefixture I0 should rise above the predetermined value the compressor isplaced in operation regardless of the temperatures within the fixtures II and I2 so that the existence of high temperatures in the fixture I0 isprevented. Electrodes 45 of the thermostatic control means 32 and 33operate in exactly the same way as the' electrodes 45 of any of thethermostatic control means also completes a maintaining circuit which isindependent of the contact members 66 and 85 and the contacts 65 and 84,and this maintaining circuit may be traced from the line wire I06 towires IIO, III and H2, electrodes 43 and 45, wires I36 and I23, contact84, contact member 82, terminal 83, conductor I24, terminal 64, contactmember 63, contact 62, bridge member 6|, conductor I34, contact 99,bridge member 98, contact I 00, conductor I26, contacts 92 and 93,conductor I21, operating coil 91, conductor I28, and terminal I05 backto the other line wire I01. Accordingly, the compressor is maintained inoperation until all of the electrodes 45 of the thermostatic controlmeans are unbridged or until the suction pressure decreases to 10 lbs.or until the head pressure increases to 190 lbs.

From the above it is seen that this invention contemplates a controlsystem for a refrigerating apparatus wherein the compressor cannot bestarted until the head pressure decreases to a predetermined low valueof lbs., wherein defrosting of all of the evaporators during each cycleof operation of the compressor is provided since it is impossible tostart the compressor until the suction pressure increases to adefrosting valueof 35 lbs., and wherein the compressor is started whenthe temperature in all of the fixtures increases to a predeterminedvalue, illustratively 42. By preventing during the normal operation ofthe system starting of the compressor until the temperature in all ofthe fixtures increases to 42, the fixtures tend to heat and coolsubstantially simultaneously so that stopping of the compressor andhence periodic defrosting of all of the evaporators is assured. If dueto an increase in load in any of the fixtures which causes thetemperature in that fixture to rise above the predetermined value tosay44, the compressor is placed in operation regardless of the temperaturein the remaining fixture providing the evaporators of all of thefixtures have defrosted. This prevents the building up of unduly hightemperatures in any of the fixtures. In each instance, when thetemperature in a fixture rises to or above the predetermined value,illustratively 42, the solenoid valve of that fixture is opened so thatrefrigerant may be supplied to the evaporator of that refrigerator whenthe compressor is placed in operation.v

Although for purposes of illustration one form of this invention hasbeen disclosed, other forms thereof may become apparent to those skilledin the art and therefore this invention is to be limited only by thescope of the appended claims and prior art.

We claim as our invention:

1. In a control system for a temperature changing system having atemperature changing apparatus for regulating the temperature of aplurality of spaces, the combination of, thermostatic means associatedwith each space and responsive to the temperature thereof, and meansincluding means controlled by the thermostatic means to operate thetemperature changing apparatus only when the temperatures of all of thespaces deviate to predetermined values and means controlled by thethermostatic means to operate the temperature changing apparatus whenthe temperature of any space deviates beyond the predetermined value.

2. In a control system for a temperature changing system havingtemperature changing means for supplying temperature changing fluid to aplurality of spaces for regulating the temperature thereof, thecombination of, thermostatic means associated with each space andresponsive to the temperature thereof, valve means associated with eachspace for controlling the supply of temperature changing fluid to thatspace, and means including means controlled by the thermostatic meansfor operating the temperature changing means only when the temperaturesof all of the spaces deviate to predetermined values, means controlledby the thermostatic means for operating their associated valve means tosupply temperature changing fluid to the associated spaces when thespace temperatures deviate to the predetermined values and meanscontrolled by the thermostatic means for operating the temperaturechanging means when the temperature of any space deviates beyond thepredetermined value.

3. In combination, a plurality of heat exchangers for regulating thetemperature in a plurality of spaces, means for supplying temperaturechanging fluid to said heat exchangers, thermostatic means associatedwith each space and responsive to the temperature thereof, valve meansassociated with each heat exchanger for controlling the supply oftemperature changing fluid thereto, and means including means controlledby the thermostatic means for operating said supplying means only whenthe temperatures of all of the spaces deviate to predetermined values,means controlled by the thermostatic means for operating theirassociated valve means to supply temperature changing fluid to theassociated heat exchangers when the space temperatures deviate to thepredetermined values and means controlled by the thermostatic means foroperating said supplying means when the temperature of any spacedeviates beyond the predetermined value.

4. In a control system for a cooling apparatus for cooling a pluralityof spaces, the combination of, thermostatic means associated with eachspace and responsive to the temperature thereof, and means includingmeans controlled by the thermostatic means to operate the coolingapparatus only when the temperatures of all of the spaces increase .topredetermined values and means controlled by the thermostatic means tooperate the cooling apparatus when the temperature of any spaceincreases above the predetermined value.

5. In a control system for a refrigerating apparatus having a compressorand a plurality of evaporators for cooling a plurality of fixtures, thecombination of, thermostatic means associated with each fixture andresponsive to the temperature thereof, and means including meanscontrolled by the thermostatic means for operating the compressor tosupply refrigerant to all of the evaporators only when the temperaturesof all of the fixtures increase to predetermined values and meanscontrolled by the thermostatic means of any fixture for operating thecompressor to supply refrigerant to its associated evaporator when thetemperature of that fixture increases above the predetermined value.

6. In a control system for a refrigerating apparatus having a compressorand a plurality of evaporators for cooling a plurality of fixtures, thecombination of, thermostatic means associated with each fixture andresponsive to the temperature thereof, valve means associated with eachevaporator for controlling the flow of refrigerant therethrough, meanscontrolled by each thermostatic means for operating its associated valvemeans to permit flow of refrigerant through its associated evaporatorwhen the temperature of that fixture rises to 01' above a. predeterminedvalue, and means including means controlled by 'the thermostatic meansfor operating the comincrease to said predetermined values and meanscontrolled by the thermostatic means of any fixture for operating thecompressor when the temperature of that fixture increases above thepredetermined value whereby refrigerant is supplied to the evaporator ofthat fixture.

7. In a control system for a refrigerating apparatus having a compressorand a plurality of evaporators for cooling a plurality of fixtures, thecombination of, thermostatic means associated with each fixture andresponsive to the temperature thereof, control means controlled by acondition which is a measure of the temperature of the evaporators, andmeans including means controlled by the control means and thethermostatic means for operating the compressor to supply refrigerant tothe evaporators only when the evaporators have defrosted and when thetemperatures of all of the fixtures increase. to

predetermined values and means controlled by the control means and thethermostatic means of any fixture for operating the compressor when theevaporators have defrosted and the temperature of that fixture increasesabove the predetermined value.

8. In a control system for a refrigerating apparatus having a compressorand aplurality of evaporators for cooling a plurality of fixtures, thecombination of, thermostatic means associated with each fixture andresponsive to the temperature thereof, valve means associated with eachevaporator for controlling the flow of refrigerant therethrough, meanscontrolled by each thermostatic means for operating its associated valvemeans to permit flow of refrigerant through its associated evaporatorwhen the temperature of that fixture rises to or above a predeterminedvalue, control means controlled by a condition which is a measure of thetemperature of the evaporators, and means including means controlled bythe control means and the thermostatic means for operating thecompressor to supply refrigerant to the evaporators only when theevaporators have defrosted and when the temperatures of all of thefixtures increase to the predetermined values and means controlled bythe control means and the thermostatic means of any fixture foroperating the compressor when the evaporators have defrosted and thetemperature of that fixture increases above the predetermined value.

9. In a control system for a refrigerating apparatus having a compressorand a plurality of evaporators for cooling a plurality of fixtures, thecombination of, thermostatic means associated with each fixture andresponsive to the temperature thereof, control means controlled by thepressure on the high pressure side of the refrigerating apparatus, andmeans including means controlled by the control means and thethermostatic means for operating the compressor to supply refrigerant tothe evaporators only when the head pressure has'decreased to apredetermined value and when the temperatures of all of the fixturesincrease to predetermined values and means controlled by the controlmeans and the thermostatic means of any fixture for operating thecompressor when the head pressure has decreased to the predeterminedvalue and the temperature of that fixture increases above thepredetermined value.

10. In a control system for a refrigerating apparatus having acompressor and a plurality of evaporators for cooling a plurality offixtures, the combination of, thermostatic means associated with eachfixture and responsive to the temperature thereof, valve meansassociated with each evaporator for controlling the flow of refrigeranttherethrough, means controlled by each thermostatic means for operatingits associated valve means to permit flow of refrigerant through itsassociated evaporator when the temperature of that fixture rises to orabove a predetermined value, control means controlled by the pressure onthe high pressure side of the refrigerating apparatus, and meansincluding means controlled by the control means and the thermostaticmeans for operating the compressor to supply refrigerant to theevaporators only when the head pressure has decreased to a predeterminedvalue and when the temperatures of all of the fixtures increase to thepredetermined values and means controlled by the control means and thethermostatic means of any fixture for operating the compressor when thehead pressure has decreased to the predetermined value and thetemperature of that fixture increases above the predetermined value.

11. In a control system for a refrigerating apparatus having acompressor and a plurality of evaporators for cooling a plurality offixtures, the combination of, thermostatic means associated with eachfixture and responsive to the temperature thereof, control meanscontrolled by a condition which is a measure of the temperature of theevaporators, control means controlled by the pressure on the highpressure side of the refrigerating apparatus, and means including meanscontrolled by both control means and the thermostatic means foroperating the compressor to supply refrigerant to the evaporators onlywhen the evaporators have defrosted, when the head pressure hasdecreased to a predetermined value and when the temperatures of all ofthe fixtures increase to predetermined values and means controlled byboth control means and the thermostatic means of any fixture foroperating the compressor when the evaporators have defrosted, when thehead pressure has decreased to the predetermined value and when thetemperature of that fixture increases above the predetermined value.

12. In a control system for a refrigerating apparatus having acompressor and a plurality of evaporators for cooling a plurality offixtures, the combination of, thermostatic means associated with eachfixture and responsive to the temperature thereof, valve meansassociated with each evaporator for controlling the flow of refrigeranttherethrough, means controlled by each thermostatic means for operatingits associated valve means to permit flow of refrigerant through itsassociated evaporator whenthe temperature of that fixture rises to orabove a predetermined value, control means controlled by a conditionwhich is a measure of the temperature of the evaporators, control meanscontrolled by the pressure on the high pressure side of therefrigerating apparatus, and means including means controlled by bothcontrol means and the thermostatic means for operating the compressor tosupply refrigerant to the evaporators only when the evaporators havedefrosted, when the head pressure has decreased to a predetermined valueand when the temperatures of all of the fixtures increase to thepredetermined values and means controlled by both control means and thethermostatic means of any fixture for operating the compressor when theevaporators have defrosted, when the head pressure has decreased to thepredetermined value and when the temperature of that fixture increasesabove the predetermined value.

13. In a control system for a refrigerating apparatus having acompressor and a plurality of evaporators for cooling a plurality offixtures, the combination of, thermostatic means associated with eachfixture and responsive to the temperature thereof, control meansresponsive to variations in suction pressure, and means including meanscontrolled by the control means and the thermostatic means for operatingthe compressor to supply refrigerant to the evaporators only whensuction pressure increases to a predetermined value and when thetemperatures of all of the fixtures increase to predetermined values andmeans controlled by the control means and the thermostatic means of anyfixture for operating the compressor when the suction pressure increasesto the predetermined value and the temperature of that fixture increasesabove the predetermined value.

14. In a control system for a refrigerating apparatus having acompressor and a plurality of evaporators for cooling a plurality offixtures, the combination of, thermostatic means associated with eachfixture and responsive to the temperature thereof, valve meansassociated with each evaporator for controlling the flow of refrigeranttherethrough, means controlled by each thermostatic means for operatingits associated valve means to permit flow of refrigerant through itsassociated evaporator when the temperature of that fixture rises to orabove a predetermined -value, control means responsive to variations inWILLIAM J. MCGOLDRICK. ALWIN B. NEWTON.

